The present invention relates to rigid, aromatic polyimide compositions having improved oxidative stability and surprisingly excellent tensile properties. More particularly, the invention resides in the discovery that such rigid, aromatic polyimide compositions can be prepared by a solution imidization process.
Typically, aromatic polyimide compositions have been prepared by solution imidization as described in a U.S. Pat. No. 3,179,631 to Endrey, and U.S. Pat. No. 3,249,588 to Gall. These previous polyimide compositions, with high thermal stability and overall mechanical properties, have found wide acceptance as coatings, films and fabricated parts used in technically demanding environments such as plasma chambers, jet engines, business machines, automotive components and diverse industrial equipment.
Rigid, aromatic polyimide compositions, on the other hand, have heretofore been made by solid state imidization after precipitation of the polyamic acid intermediate as described in U.S. Pat. No. 5,162,492 to Kaku. In Kaku, the solid state imidization process was used to react 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA) and m-phenylene diamine (MPD) to produce a rigid, aromatic polyimide composition having hydrolytic and oxidative stability. It is known, however, that rigid, aromatic polyimide compositions are typically too crystalline when they are imidized in solution, which results in very poor properties. No solution imidization process has ever been successfully used to make rigid, aromatic polyimide compositions having acceptable properties.
Despite the excellent performance characteristics of previously available polyimide compositions, effort has been directed toward further improvement of the resistance of articles made from polyimide compositions to high temperature oxidative environments, such as those found in semiconductor etch chambers and gas turbine engines. Additionally, the solution imidization process is easier and is a less expensive process for producing polyimide compositions.